CVE-2018-18558 in ESP-IDF
Summary
by MITRE
An issue was discovered in Espressif ESP-IDF 2.x and 3.x before 3.0.6 and 3.1.x before 3.1.1. Insufficient validation of input data in the 2nd stage bootloader allows a physically proximate attacker to bypass secure boot checks and execute arbitrary code, by crafting an application binary that overwrites a bootloader code segment in process_segment in components/bootloader_support/src/esp_image_format.c. The attack is effective when the flash encryption feature is not enabled, or if the attacker finds a different vulnerability that allows them to write this binary to flash memory.
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Analysis
by VulDB Data Team • 09/15/2023
The vulnerability identified as CVE-2018-18558 affects Espressif ESP-IDF versions 2.x and 3.x prior to specific patches, representing a critical security flaw in the bootloader implementation that undermines the device's secure boot mechanism. This vulnerability resides within the second stage bootloader component of the ESP-IDF framework, specifically in the process_segment function located in components/bootloader_support/src/esp_image_format.c. The flaw stems from inadequate input validation during the processing of application binaries, creating a pathway for malicious code execution that bypasses fundamental security protections designed to prevent unauthorized software from running on embedded devices. The vulnerability is particularly concerning because it allows an attacker with physical proximity to the device to execute arbitrary code, significantly expanding the attack surface beyond traditional network-based threats.
The technical exploitation of this vulnerability occurs through the manipulation of application binary files that can overwrite critical code segments within the bootloader itself. When the bootloader processes these crafted binaries, it fails to properly validate the input data, allowing malicious code to be written over legitimate bootloader instructions. This type of vulnerability aligns with CWE-129, which describes insufficient input validation, and specifically relates to CWE-787, representing out-of-bounds write vulnerabilities that can lead to code execution. The attack vector requires physical proximity to the target device, making it a local privilege escalation or lateral movement threat that can be particularly dangerous in environments where physical security is compromised or when devices are deployed in accessible locations.
The operational impact of this vulnerability extends beyond simple code execution, as it fundamentally undermines the secure boot chain that is critical for embedded device security. When flash encryption is not enabled, or when attackers can leverage other vulnerabilities to gain write access to flash memory, this flaw becomes exploitable through a combination of physical access and potentially other attack vectors. The vulnerability demonstrates the importance of secure bootloader implementation in embedded systems and highlights how seemingly minor input validation issues can have catastrophic consequences for device security. This weakness enables attackers to potentially install backdoors, modify firmware, or execute malicious payloads that can persist across device reboots, making it a particularly dangerous vulnerability for IoT devices and embedded systems where long-term security is paramount. The attack scenario described aligns with ATT&CK technique T1059.001, which covers command and script interpreter execution, and T1068, covering exploit for privilege escalation, both of which can be facilitated through this bootloader compromise.
Mitigation strategies for CVE-2018-18558 should focus on immediate firmware updates to patched versions of ESP-IDF, specifically versions 3.0.6 and 3.1.1 or later, which address the input validation deficiencies in the bootloader component. Organizations should implement robust physical security measures to prevent unauthorized access to devices, as the vulnerability requires physical proximity to exploit effectively. Additionally, enabling flash encryption where possible and implementing additional security controls such as secure boot verification and integrity checking can provide defense-in-depth protection against similar vulnerabilities. Regular security assessments of embedded systems should include thorough analysis of bootloader components and input validation mechanisms to identify and remediate similar weaknesses before they can be exploited by adversaries. The vulnerability serves as a reminder of the critical importance of secure bootloader implementation in embedded systems and the need for comprehensive security testing throughout the development lifecycle to prevent such fundamental security flaws from reaching production environments.